Fire station retrofit Case study
Data
Fire station’s projected improvements
Design consultant: Scott
Wilson
M&E Engineer: JSMS Ltd
Total project cost: £1.3m.
Fuel savings of £7,200 a year predicted
Display energy certificate:
projected improvement from D90 to B25
Boilers: two 45 kWh biomass boilers with a 600 litre thermal store provide all heating and hot water
Overall heat load:
expected to fall from 425,000 KwH to 86,200 KwH. All energy use to be compared against historic data
Lighting controls: high
frequency lamps with occupancy and daylight control in all areas of the building. Expected to save 30% of electricity load
Insulation materials: in
both the walls and roof. Chosen for their minimal environmental impact with zero ODP and low GWP
Photovoltaics: 14.4kWp
of PV mounted in four strings on the appliance bay and main building roof. Currently contributes 6% to 7% of electricity, short of eight per cent projected, with shortfall attributed to poor weather
Windows: double glazing with low emissivity glass
Projected improvement in U-values (W/sq m K):
Roof: 2.502 to 0.24 = 90% Walls: 1.58 to 0.548 = 65% Cladding: 2.37 to 1.2 = 49% Windows: 5.7 to 1.2 = 78%
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Photovoltaic solar cells on the roof provide about 7 per cent of the station’s electricity needs.
Photovoltaics
Conventional electricity supplies have been supplemented with 14.4 kWp (kilowatt peak) of photovoltaic (PV) cells mounted on roof areas of the fire station. Shaw hopes the cells will provide 8 per cent of the station’s annual electricity consumption, although he admits that the current contribution is closer to 6 to 7 per cent, which he blames on poor weather. The existing Automatic Meter Reading for electricity
has been supplemented with remote logging of the PV system, so that comparisons can be made between predicted and actual outputs in real time. A grant of £40,000, half the total cost of the PV
system, was obtained through the government’s Low Carbon Buildings Programme. Shaw admits PV is expensive but argues: ‘On a fire station you want something simple that no one has to bother with. There are no maintenance costs; you put it on the roof, plug it in and it works.’
Insulation
While the London Fire Brigade is enthusiastic about renewable energy, Bentley would advise anyone attempting a low-carbon refurbishment to focus first on insulation and air tightness: ‘It’s the most effective thing you can do.’ The U-values of the roof have been improved 90 per
cent, from 2.502 to 0.24 W/sq m K, while the walls, to which cavity wall insulation was added, have improved 65 per cent, from 1.58 to 0.548 W/sq m K. The U-value of the cladding that covers several of the station walls has improved 49%, from 2.37 to 1.2 W/sq m K. Bentley says extra insulation was added, above and
beyond the original design specification, to voids in the wall cladding that were discovered as the building work progressed. ‘Obviously you end up with a bigger bill, but you won’t get another opportunity to do it for 30 years, so there’s no point leaving it,’ Bentley reasons. The U-values of the windows were improved 78per cent, from 5.7 to 1.2 W/ sq m, after single-glazed, wood-
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CIBSE Journal April 2010
and-steel windows were replaced with aluminium- framed, double-glazed windows made with low- emissivity glass.
Materials
Bentley tried hard to use materials with low embodied carbon and consulted the University of Bath, which publishes a free online database of embodied energy and carbon for building materials (https://wiki.bath. ac.uk/display/ICE/Home+Page). He was mostly successful; the only high-carbon element in the Croydon refurbishment is the aluminium frames for the windows and the rainwater cladding on the walls, he says, although he rues the fact that there is no low- energy glass available currently. Bentley is frustrated by what he sees as secrecy
and obfuscation among manufacturers on the issue: ‘There is no pressure on the industry to bring down the embodied energy in its products. Manufacturers will not tell you how much embodied carbon is in them.’ Following the refurbishment, Shaw is hoping to
achieve an improved display energy certificate (DEC) rating of B25, compared with D90 before the work started. He calculates that the building’s overall heat load has been cut from 425,000 kwH down to 86,200 kwH, based on the new U-values compared with the previous ones. Bentley explains that the projected savings are based
on the actual heat requirements of the old building, measured using the metered gas supply to the old heating boilers, including an assumed percentage efficiency, compared to the new heating requirements for the new insulated buildings. These figures were compared with the results from the SBEM calculations to give a reality check. Shaw will be monitoring the results, using the
automatic meters for the electricity and biomass boilers and comparing the data against the historic data on gas and electricity usage. ‘I have personal targets to make sure these things work,’ says Shaw. l
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